This invention relates to roof coverings, and more particularly to sheet products useful in such coverings.
U.S. Pat. No. 4,468,422, xe2x80x9cMaterial Useful As Roofingxe2x80x9d, Siener, Jr. et al., granted Aug. 28, 1984, taught including, along one warp-direction edge of sheet roofing, low-elongation aramid reinforcing strands, in a weft-inserted reinforcing fabric sandwiched between two chlorinated polyethylene plastic layer portions, for holding down by plates spaced along the same direction, to improve wind uplift resistance. That patent also taught use of polyester strands of 1000 denier as other reinforcing threads in the warp direction, and doubletons in the fill. Said patent is hereby incorporated by reference herein.
Also known in the prior art are roofing sheet panels in which the two layer portions of plastic formed into single-ply are polypropylene, sandwiching a layer of weft-inserted reinforcing fabric, in which both warp and fill are of polyester singleton threads all alike.
More than a year ago, our company (assignee hereof) sold roof panels in which layer portions of polyvinyl chloride created a single-ply sandwich with a low-stress weft-inserted reinforcing fabric layer which included a mounting area immediately adjacent a warp edge and strengthened against elongation by inclusion of, for a four-inch width, alternating warp xe2x80x9cthreadsxe2x80x9d of 1500 denier aramid singletons and 2000 denier (paired 1000""s) high breaking tenacity polyester doubletons. The warp threads outside the mounting area were 1000 denier high breaking tenacity polyester singletons. All the fill threads were doubletons of that same polyester yarn (making each of these effectively threads, using xe2x80x9cthreadxe2x80x9d as xe2x80x9cknitted as onexe2x80x9d, and so treated in xe2x80x9cthread countxe2x80x9d and so used herein throughout) of 2000 denier. Thread count was 9xc3x979 throughout. Factory Mutual Company in December, 1997 approved this product with an I-90 (pounds per square foot of uplift) wind resistance rating with hold-down fasteners spaced twelve inches apart. (This sale was regarded as experimental, although the customer was not so informed, and is not conceded to be relevant prior art.)
This invention is based in one aspect on the discovery that, for a reason or reasons not fully understood, strands of ultra-high-molecular-weight polyethylene (UHMWPE) provide, when included as reinforcing strands in narrow mounting areas along edges of panels of sheet roofing, exceptionally useful aid in increasing wind uplift resistance, particularly with polypropylene as the single-ply plastic.
In preferred embodiments, the sheet of the invention is of single-ply polypropylene, in which is intermediately embedded a reinforcing low-stress weft-inserted fabric in which the mounting area is along a longitudinal, warp-thread directional, edge of each panel, of width slightly greater than the outside diameter of hold-down ring-edged xe2x80x9cpressure platesxe2x80x9d that engage it; the UHMWPE threads are warp strands and the mounting area includes also warp threads of lower tenacity and lower breaking strength, fill threads being throughout the sheet of lesser xe2x80x9ctenacityxe2x80x9d (i.e., as used herein throughout, breaking tenacity) than the UHMWPE strands.
In another aspect, the invention provides such sheet roofing panels in which the fabric layer of a single-ply sandwich comprises three reinforcement areas: a mounting edge area with first and second threads extending in a direction corresponding to that of a row of fasteners for hold-down units and respectively of a first higher tenacity and a second lower tenacity; a second area corresponding to the locus of all reinforcing threads outside said mounting edge area and including third threads parallel with said first threads and in which said third threads are of a second, lower tenacity and a first lower breaking strength; and a third area consisting of the entire panel, and in which fourth reinforcing threads are perpendicular to said first and second threads and are of said lower tenacity but of a second higher breaking strength.
In most preferred embodiments in this aspect, the first threads are of UHMWPE, alternating with threads of polyester doubletons, the third threads are polyester singletons, and the fourth are polyester doubletons; and thread count is uniform and 9xc3x979 throughout.
There follows a description and drawing of the presently preferred embodiment.